The US will not reveal whether it has received a request to extradite Amanda Knox after her murder conviction was upheld.

The 26-year-old, who lives in Seattle, faces a 28-and-a-half year jail sentence after an Italian court reinstated the guilty verdicts against her and her former boyfriend Raffaele Sollecito.

They are accused of killing 21-year-old British student Meredith Kercher in 2007.

The State Department's deputy press secretary Marie Harf said: "We've been following it closely as it's gone through the Italian legal system.

Image Caption:Knox wiped away tears during a TV interview in the US

"I don't have any more analysis of the Italian judicial procedure for you. But again, we'll just keep monitoring it and if we have anything else to say as we get further along in the process, we will.

"Extradition requests I understand, are legally private and confidential, so I don't think I have more comment than that. We do have an extradition treaty, which has been in force since 1984."

On Friday, Knox wept on television as she vowed to fight her latest conviction for the murder of Miss Kercher "to the very end".

She broke down several times in the TV interview and said: "This really has hit me like a train."

She made it clear she would never voluntarily return to Italy to serve the sentence handed down by a court in Florence.

Legal experts say there is no reason why the US should refuse Italy's request, meaning Knox could be jailed in Italy.

Lyle Kercher, Meredith's brother, said: "If somebody's found guilty and convicted of a murder - if an extradition law exists between those two countries - I don't see why they (the US) wouldn't.

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"It would set a difficult precedent if a country such as the US didn't choose to go along with laws they themselves uphold when extraditing convicted criminals from other countries."

Sollecito, who was not in court for the verdict but had attended lengthy hearings earlier in the day, was sentenced to 25 years.

The 29-year-old has been held by Italian police after being stopped near the country’s border with Austria on Friday morning.

Lawyers for Knox and Sollecito have said they intend to appeal to Italy's highest court and a long legal battle for Knox's extradition is expected.

Knox and Sollecito were charged in 2007 after Miss Kercher's semi-naked body was found with her throat cut in the bedroom of the house she shared with Knox in the central Italian city of Perugia.

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The Leeds University student from Coulsdon, Surrey, had been sexually assaulted.

Two years after the pair were found guilty at their original trial in 2009 - and handed jail terms totalling more than 50 years - the verdicts were overturned and both walked free from court, with Knox returning to the US and going on to sign a book deal.

Their acquittals in 2011 came after a damning 100-page report outlined a catalogue of errors and breaches of procedure that had been made in collecting evidence.

The third trial began last September in Florence.

After nearly 12 hours of deliberations on Thursday, the court upheld the 2009 convictions.

Drug dealer Rudy Guede was sentenced to 16 years for Miss Kercher's murder. Investigators said he did not act alone.